Human malaria is exclusively vectored by anopheline mosquitoes. In southern Africa the most important of these vector species are An. arabiensis, An. gambiae, and An. funestus, with An. arabiensis having a wider range and considerably greater ecological and biological plasticity. The relative distribution and abundance of these vectors vary ecologically and geographically. The study sites targeted in this proposal not only reflect differences in malaria transmission biology and intensity, but also ecological differences that affect these vector differences. Transmission biology is largely affected by mosquito behavior and their response to mosquito-based control measures such as insecticide-treated bed nets (ITNs). ITNs are widely distributed throughout south Africa and represent an enormous investment. ITNs not only provide a physical barrier to mosquitoes, but it is also well known that ITNs repel insects, encouraging mosquitoes to feed on alternative hosts. In some areas of southern Africa, however, mosquitoes have continued to almost exclusively target human hosts, despite the distribution and use of ITNs. Recent data from West Africa have shown that in some areas the repellency, typically induced by ITN use, fails and resistant mosquitoes are not deterred from taking human blood meals. Therefore, understanding the bionomics, foraging behavior, levels of insecticide resistance and population genetics and distribution are integral for guiding selection and implementation of effective and appropriate malaria interventions within the southern African region. Aim 1) Characterize the bionomics and entomological inoculation rates (EIR) of malaria vectors in each of the three study sites. Characterize the community structure of malaria vector populations in southern Africa and further characterize the feeding and resting behavior of Anopheles arabiensis in southern Africa. Aim 2) Survey insecticide susceptibility of vector populations at all three field sites and to determine the mechanisms of insecticide resistance. Aim 3) Conduct population genetic analysis of Anopheles arabiensis populations using single-nucleotide polymorphism (SNP) markers.